Safety device for electrical apparatus



Sept 15, 1931- c. B. BRAESTRUP 1,322,919

SAFETY DEVICE FOR ELECTRICAL APPARATUS Filed Nov. 25, 1929 S lo s711719; [IAM 2 I www "if" NvENToR Carl B. mesimp A qz/ HIS ATTO YS Patented Sept. 1-5, 1931 PATENT OFFICE CARL B. BRAESTRUP, OF SCARSDALE, NEW YORK SAFETY DEVICE FOR ELECTRICAL APPARATUS Application filed November 25, 1929. Serial No. 409,458.

. This invention relates to a safetyor protective device for electrical apparatus.

I have seen iit to illustrate my invention as embodied in X-ray mechanism to protect the X-ray tube from excessive temperatures, but I wish it to be understood that I contemplate its use with other types of electrical apparatus which are subject to high temperature either because of excessive current flow, l@ mechanical friction, such as is present in an ordinary bearing7 or heat radiation from a heating coil, arc or filament.

It is an object of this invention to produce a safety device which is susceptible of actui ation due to direct transmission of heat from 'feg a Lready market.

Further features and objects of the invention will be more fully understood from the following detail description of the accompanying drawings, in which f Fig. 1 illustrates a simple, electrical circuit for 'an X-ray tube and' shows the relative Npoition of the safety device and X-raytube, an

Fig. 2 is a sectional side elevation of the .safety device.

Looking at Fig. l, wires l and Q'represent the low v voltage primary circuit which may be varied from zero to a maximum value of about 220 volts, depending upon the size and 'type of X-ray 'apparatus utilized and the class of lwork desired to accomplish. T represents a high tension transformer, wherein 3 illustrates the primary windings connected to the low voltage 'wires l and 2, and 4 repings adapted to be connected to the X-ra-y tube. One side of the secondary or high tension circuit is connected by means of Wire 6 to the cathode terminal 7 of. the tube X, this cathode terminal 7 is usually made in the'55 form of a screw so that the tube may be conveniently secured into an electric socket. The terminal 7 is connected to the cathode C within the evacuated glass bulb of the tube X. The other side of the secondary or high 6o tension windings 4 is connected by means of wire 9 to the terminal 10 of the safety devlce.

A common type of commercial X-ray tube is equipped with radiating fins R, usually in the form of thin discs attached to the extension of the anode A which extends outwardly from the evacuated glass portion of the tube. These radiator fins or discs, as the name would imply, are for the purpose of'fo dissipating the heat generated at the anode. The anode arm is usually made of copper and is generally a continuous piece extending through the radiator discs inwardly through the evacuated glass tube to a point oppo site and adjacent to the cathode. The bevel'edend of the anode is equipped with a tungsten target 12. With this construction the heat generated at the anode is transmitted through the copper body of the anodej S0 which is usually in the form of a stem of substantial diameter, to the radiator discs R which are cooled by the surrounding air. Radiator discs R are mounted upon a suitable sleeve adapted 'to slip over the outer end off 85 the stem of the anode and toV be secured in place by a knurled screw, axially disposed in the end of the stem. I have seen fit to design my safety device so that it may be easily and readily substituted for the screw with' which a common type of commercial tube is equipped.

It is obvious that in tubes not provided with the construction described above other suitable mounting may be provided to furnish a heat conducting path between the anode and the safety device.

This construction will be further described in the detailed description of Fig. 2.

It is suiiicient for the purpose of the de- 100 Vglass tube 15 with removable metal spring clip heads 16 and 17 which may be pulled off of the glass tube for the purpose ofreplacing the fusible element ofthe safety device, as Y ,will be explained more ful-ly hereafter.

Head 16 is equipped with a terminal device 'shown in the fiorm of adouble ringI shaped substantially in the.v form of a figure 8: and

y 'adaptedtopass through aperture 11S-in head 16# and?v illustrated with the" circular porti'on 195 onthe outside of the'head 16 and ay circular or hooked portion 20 on the ins-ide v thereof. Y

Head? 1'? is secured to a k-nur-led nut 21v by means ofi' ascrew 22fwhich is adapted. tofpass through.. the head 17 and nut 21 andI extended vfor a substantial distance beyond", say about f/gmsothat screw 22 may be screwed into the threaded Vhole furnished in the outer end of the anode stem; in placeof'the screw which is iisedfrtoy hold' the radiator discs in place,

I andthus the safety device-may be readily secured teltlefend of' the anodey stem adjacent 'to the radiator discs and; will serveV to hold the radiator discs inplace instead of the Ausualfserew furnishedfor that purpose. rllhe knurled nutl willv serve to enable an operator y tofVVscrew the vsafety device into-place. 'The head-of screw V22'isV furnished? with the usual "illustrated inV-the'form of a washer 26; The

slot aiidfin sai'd'- slotis soldered by means of a metal25 oflow melting point a link herein metal' 25 should possess a sufficiently low melting point so that heat (transmitted through they anodefr andscrew 22 will melt "the metal 25 before the anode'A'. reaches a dangerouslvhigh temperature. The spring 30 joins the hook 20- of" terminal" l0 to the washer or link 261` and is 'so ,calibrated as tonormally/eXert a tension on cl the' link' 26'V when the spring is ini; the position f -t/Vhen'Xfray tubesare subjected to an eX- jcessive current for are continuously utilized for a long period of time, the anode A is apt tobecome soA hot as` to'permanentlyimpair the'functioiiI ofthe X-ray tube and even cause the tungsten target 12 to drop out of Y the bevelediendthereof-and thus cause breakage off'thevtube which. is avery undesirable fthing because X-rayA 'tubes are very eX- pensive; Y Y v ith my safetvdevice the heat generated Yat' tlieanode willffbe transmittedfthrougli the stem, of the anode `tol-the outer end thereof andlthroughthe-metallicscrew 22-to the fusible metal 25 which will melt and releasek the link 26 which will be drawn toward the terminal 10 or kto the left, as viewed in Fig. 2, and when this device is installed onan X-ray apparatus where a high voltage and low amperage is used, the length of the device may be such.` tlia-t an arc will be drawn fromA` thehead of theV screw 22 tor the link 26 after it has been released and pulled by the Vspring toward the left, and this arc will be vice withy replaceable portions consisting of screw 22, and link 26 inset'in; fusible metal 25, sothat the operator may refill the safety device in its original condition by'merely removing` it `from the tube,` disengaging the headl 17 andl the members attached thereto and replacing; screw 22: and link'26. soldered thereinwhich maybe hooked to the springjO by pulling the spring 30 outwardly by means of hooked wire or button-hook, for'instance. In this manner the safety device may-be readily and quickly reassembled` atl aznii'niniuincost and expense.V f i 1 The' length of time required to.y replace the screw and link is desirable rather than undesirable, as it forces the operator to allow the tube to-stand` long enough to cool oft.

If my safety device is installed` with some other type of electricah apparatus wherein a. lower voltage and perhaps' a higher amperage is utilized, it may' not be desirable to designf the glass body portion, 15 so that an arcwill be drawn and maintainedbetween the terminals of the device, but instead` it v may be desirable merely to break theY electrical circuit so astov disconnect theV current from the apparatus. This resultl of course,

may be obtainedby the same construction illustratedv inthe figures andY described' above.

Whereas, I have described my invention. Y by reference toYV specilic'forms thereofgi. it will be understood thatniany changes and modilications may be made without departing from the spirit of the invention.` V Y In safety device for an Xray tube, a body 'having a transparent portion, a fusible link in said body connected into and made part' of the electric circuit for carryiiigthe current for the tube, a metallic screw attachedtosaid fusible linkfandadapt'ed to passthroughand project Vfrom said safety device so that'a con# siderableportion thereofV may.Y be screwed Y intovtlie anode stem of'an X-ray tube. ahead on said screw having'a slot'inwhichtlie fusible metal of:l said linkA bev disposedto produce a, close and intimate contact between said meta-l5 andi screw `to facilitatek the transmission of heat fromA the latter tothe former," a springinsaid body connected` to -saifd 

